white stain

I have been doing windows off and on for a couple years now. I sometimes finish up with a pale white 'drip' stain on the upper part of the glass. I have tried to rewash , it still does not come off. I have tried to 'buff' with a clean cloth, nothing seems to remove these 'stain's. I usuall use liquid dish detergent or amonia, usually amonia. Any suggestions ?
Thanks !
Barry

They may be hard water spots! If so, you can remove them with lime away. Spray it on light scrub. Then wash it.

Hi Dan, Thanks for replying. I wonder if there is anything I can add to my water prior to washing the glass that would eliminate these spots ?
Thanks .
Barry

Not sure! When I see it I just pull out the lime away.